System including an indicator responsive to an electret for a power bus

ABSTRACT

An indicator system for an alternating current power bus includes an electret operatively associated with the alternating current power bus. The electret includes an output having an alternating current voltage when the alternating current power bus is energized. A rectifier includes an input electrically interconnected with the output of the electret and an output having a direct current voltage responsive to the alternating current voltage of the output of the electret. An indicator includes an input electrically interconnected with the output of the rectifier and an indication output responsive to the direct current voltage of the output of the rectifier.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to commonly assigned, copending U.S. patentapplication Ser. No. 13/241,862, filed Sep. 23, 2011, entitled “POWERSYSTEM INCLUDING AN ELECTRET FOR A POWER BUS”.

BACKGROUND

1. Field

The disclosed concept pertains generally to power bus apparatus and,more particularly, to power systems including an alternating currentpower bus. The disclosed concept also pertains to indicator systems foran alternating current power bus.

2. Background Information

Inside of electrical control centers, as well as other electricalenvironments, there are bus bar wiring conductors and lugged cableconnection conductors, as well as conductor taps for three-phase power.This is true regardless whether the corresponding electrical product isfor low-voltage or for medium-voltage.

Maintenance personnel can be harmed when accidentally touching energizedsurfaces of power bus bars.

Electrical sensors of various types are used to detect the currentflowing through a conductor. Such sensors include, for example, a singleHall effect sensor that produces an output voltage indicative of thecurrent magnitude as well as more conventional current sensors such as ashunt resistor or a current transformer.

Hall effect devices have been used to sense variations in magnetic fluxresulting from a flow of current through a conductor. Some of theseknown devices have used a flux concentrator to concentrate magnetic fluxemanating from the flow of current through the conductor. It haspreviously been suggested that electrical current sensing apparatuscould be constructed in the manner disclosed in U.S. Pat. Nos.4,587,509; and 4,616,207.

It is also known to measure the current in a conductor with one or twoappropriately placed Hall sensors that measure flux density near theconductor and to convert the same to a signal proportional to current.See, for example, U.S. Pat. Nos. 6,130,599; 6,271,656; 6,642,704; and6,731,105.

U.S. Pat. No. 7,145,322 discloses a power bus current sensor, which ispowered by a self-powered inductive coupling circuit. A sensor sensescurrent of the power bus. A power supply employs voltage produced bymagnetically coupling the power bus to one or more coils, in order topower the sensor and other circuitry from flux arising from currentflowing in the power bus.

U.S. Patent Application Pub. No. 2007/0007968 discloses a system formonitoring an electrical power system including one or more transducerunits, each of which has a current measuring device and a voltagemeasuring device coupled to a respective one of the phase conductors ofthe power system, and a transducer wireless communications device. Thetransducer unit includes a battery for providing power to the componentsthereof. The battery is connected to a trickle charger, which, in turn,is electrically coupled to a phase conductor. The trickle charger is aknown parasitic power charger that draws power from the phase conductorand uses it to charge the battery.

A known prior proposal for monitoring a bus bar wiring conductor employsa current transformer to harvest energy or an associated signal, throughcoupling to the magnetic field caused by current flowing through theconductor. However, if a load is not connected to the conductor, and,thus, no current is flowing, then a current transformer (or magneticcoupling) will not function.

There is room for improvement in indicator systems for a power bus.

There is further room for improvement in power systems including a powerbus.

SUMMARY

These needs and others are met by embodiments of the disclosed concept,which provide a system for an alternating current power bus comprisingan electret operatively associated with the alternating current powerbus and an indicator directly or indirectly responsive to the output ofthe electret.

In accordance with one aspect of the disclosed concept, an indicatorsystem for an alternating current power bus comprises: an electretoperatively associated with the alternating current power bus, theelectret comprising an output having an alternating current voltage whenthe alternating current power bus is energized; a rectifier comprisingan input electrically interconnected with the output of the electret andan output having a direct current voltage responsive to the alternatingcurrent voltage of the output of the electret; and an indicatorcomprising an input electrically interconnected with the output of therectifier and an indication output responsive to the direct currentvoltage of the output of the rectifier.

The indication output of the indicator may be active responsive to thedirect current voltage of the output of the rectifier when thealternating current power bus is energized.

The alternating current power bus may have an alternating currentflowing therethrough.

Zero current may flow through the alternating current power bus.

As another aspect of the disclosed concept, an indicator system for analternating current power bus comprises: an electret operativelyassociated with the alternating current power bus, the electretcomprising an output having an alternating current voltage when thealternating current power bus is energized; and an indicator comprisingan input electrically interconnected with the output of the electret andan indication output responsive to the alternating current voltage ofthe output of the electret.

As another aspect of the disclosed concept, a power system comprises: analternating current power bus; an electret operatively associated withthe alternating current power bus, the electret comprising an outputhaving an alternating current voltage when the alternating current powerbus is energized; and an indicator circuit comprising an inputelectrically interconnected with the output of the electret and anindication output responsive to the alternating current voltage of theoutput of the electret.

BRIEF DESCRIPTION OF THE DRAWINGS

A full understanding of the disclosed concept can be gained from thefollowing description of the preferred embodiments when read inconjunction with the accompanying drawings in which:

FIG. 1 is a block diagram of an indicator system including an electret,a rectifier and a visual indicator in accordance with embodiments of thedisclosed concept.

FIG. 2 is a block diagram of an indicator system including an electretand a visual indicator in accordance with another embodiment of thedisclosed concept.

FIG. 3 is a representation of a graphic employed by the visual indicatorof FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As employed herein, the term “number” shall mean one or an integergreater than one (i.e., a plurality).

As employed herein, the statement that two or more parts are “connected”or “coupled” together shall mean that the parts are joined togethereither directly or joined through one or more intermediate parts.Further, as employed herein, the statement that two or more parts are“attached” shall mean that the parts are joined together directly.

An “electret” is a dielectric material that has a permanent orquasi-permanent electric charge and/or dipole polarization, and also haspiezoelectric characteristics. The electret dielectric material istypically metalized for electrical connectivity and is fabricated insuch a fashion that an electric field exists within the dielectricmaterial. The electret is the electrostatic equivalent of a permanentmagnet. Electrets do not typically have the capability to generate muchcurrent but can be used to provide a reference potential difference.

As employed herein the term “switchgear device” shall expressly include,but not be limited by, a circuit interrupter, such as a circuit breaker(e.g., without limitation, low-voltage or medium-voltage orhigh-voltage); a motor controller/starter; a busway; and/or any suitabledevice which carries or transfers current from one place to another.

As employed herein the term “power bus” shall mean a power conductor; apower bus bar; a power line; a power phase conductor; a power cable;and/or a power bus structure for a power source, a circuit interrupteror other switchgear device, or a load powered from the power bus.

FIG. 1 shows an indicator system 2 for an alternating current (AC) powerbus 4. The indicator system 2 includes an electret 6 operativelyassociated with the AC power bus 4. The electret 6 includes an output 8having an AC voltage 10 when the AC power bus 4 is energized. Theindicator system 2 also includes a rectifier, such as a suitablerectifier circuit 12, having an input 14 electrically interconnectedwith the output 8 of the electret 6 and an output 16 having a directcurrent (DC) voltage 18 (e.g., without limitation, pulsed DC; full waverectified DC; full wave rectified and filtered DC) responsive to the ACvoltage 10 of the output 8 of the electret 6, and an indicator, such asthe example visual indicator 20, including an input 22 electricallyinterconnected with the output 16 of the rectifier circuit 12 and anindication output 23 responsive to the DC voltage 18 of the output 16 ofthe rectifier circuit 12.

As shown in FIG. 1, the power bus 4 (e.g., without limitation, a powerbus bar or power conductor) is energized with an AC voltage 24 (withrespect to a ground or neutral potential (not shown)). The electret 6has two output terminals 26,28 for connection to the rectifier circuit12.

In this embodiment, the electret 6, having a permanent, inherentelectrostatic field (e.g., without limitation, when coupled to anadjacent energized AC power bus 4) provides a localized circuit groundpotential from which subsequent circuitry can be referenced. When an ACfield is present, the electret 6, which has a construction containing adielectric sandwiched by metal contacts, will behave like a capacitorand will charge in the presence of the AC field to provide stored energyto the output 8. For example, the electret 6 has a combination ofcharacteristics, such as permanent charge or dipole characteristics, andcan have internal electric field storage similar to a capacitor. Butsince it also has piezoelectric characteristics, it can act in concertwith a driving AC energizing voltage to be stressed through the internalelectric field (capacitive) effect and then “rebound” through thepiezoelectric effect to then generate the corresponding output ACvoltage 10. The output voltage and current is determined by the strengthof the AC field in the proximity of the electret 6, the duration thatthe electret 6 is present within the AC field, and the distance betweenthe electret 6 and the field generating power bus 4. This output voltageis converted from AC to DC through the use of the rectifier circuit 12.The output AC voltage 10 is converted to the output DC voltage 18 by therectifier circuit 12. The output DC voltage 18 of the rectifier circuit12 then can act on the visual indicator 20 to be powered using currentor charge stored internally through the internal electret electric fieldin conjunction with the internal piezoelectric character by the electret6 in the presence of the AC field. Use of the rectifier circuit 12 toconvert the output AC voltage 10 of the electret 6 to the output DCvoltage 18 of the rectifier circuit 12 is employed when the visualindicator 20 needs to be powered by DC voltage.

The electret 6, the rectifier circuit 12 and the visual indicator 20 areelectrically “floating” with respect to the power bus 4. None of this isdirectly electrically connected to ground potential or to the bus barpotential, such that the interaction is through the power bus ACelectric field. The electret 6 is adjacent to or suitably proximate thepower bus 4. The electret 6 is not actually electrically connected tothe power bus 4, although it may be suitably mechanically attached orcoupled thereto.

The electret 6 acts as a piezoelectric which also has a permanentcharge/dipole. The electret 6 interacts with the generated AC electricfield of the power bus 4. The electret output 8 provides anelectret-generated AC voltage 10.

Example 1

The electret 6 may be an electret device. If a gap 30 is employedbetween the power bus 4 and the electret 6, then the gap distance is notcritically important. However, the closer the electret 6 is to the busbar 4, the more electric field can be harvested in order to provide morepower output. The overall electret device could be physically attachedto the power bus 4 (e.g., without limitation, employing adhesive, a boltor a clamp), in order to position it as close to the power bus 4 aspossible in order to harvest relatively more electric field. Theelectret 6 converts the AC electric field to the output AC voltage 10 ina robust yet passive manner.

Example 2

The electret 6 may be made of an electret material solution packagedwithin, for example and without limitation, a molded housing (notshown).

Example 3

The electret 6 may be made from a material selected from the groupconsisting of an organic polymer electret material, and an inorganicelectret material, although a wide range of electret materials can beemployed (e.g., without limitation, other organic materials; otherinorganic materials).

Example 4

The electret 6 is coupled to the AC power bus 4.

Example 5

The rectifier circuit 12 is selected from the group consisting of adiode, a full wave bridge, and an integrated device, although anysuitable rectifier circuit 12 can be employed, such as anotherequivalent circuit or discrete hardware. The rectifier circuit 12converts the AC output voltage 10 from the electret 6 into a DC outputvoltage 18 for the DC visual indicator 20.

Example 6

The visual indicator 20 may be “electronic paper” that provides, forexample, a non-lighted, suitably high-contrast visual indicator, such asfor example and without limitation, “printed electronics” or“electrochromatic inks” marketed by NTERA, Inc. of Radnor, Pa., or“electronic ink” marketed by E Ink Corporation of Cambridge, Mass.Electronic paper types of technology are unique in that they do not drawa significant amount of current to change contrast, only enough to turnon and off. The electronic ink technology requires a voltage input toturn on and a subsequent voltage input to turn off. Once the displayturns on, it will stay on until turned off, and a voltage or current isnot needed to sustain the display. The printed electronics orelectrochromatic inks technology behaves like a leaky capacitor andrequires a voltage input to turn on, but it will decay once the voltageis removed. This works well for the disclosed concept since the displayis desired to be on while the field is present.

The visual indicator 20 may include a display of a graphic 31 (FIG. 3)that switches on (or off) in response to the presence (or absence) ofthe DC output voltage 18, which ultimately responds to the presence (orabsence) of an AC electric field of the AC power bus 4. A non-limitingexample of the graphic 31 when switched on by the DC output voltage 18is shown in FIG. 3.

Although an example visual indicator 20 is disclosed, the disclosedconcept is applicable to a wide range of visual, audible and otherindicators driven by the rectifier circuit 12 or by the electrets 6,36of FIGS. 1 and 2. For example and without limitation, the indicator maybe a wireless device structured to report an indication that the ACpower bus 4 is energized to a remote location.

Example 7

The visual indicator 20 is powered responsive to the DC voltage 18 ofthe output 16 of the rectifier circuit 12 when the AC power bus 4 isenergized.

Example 8

Further to Example 7, the AC power bus 4 has an alternating currentflowing therethrough.

Example 9

Further to Example 7, zero current flows through the AC power bus 4.

Example 10

The visual indicator 20 may have an equivalent circuit characteristicsimilar to that of a capacitor. In combination with the rectifiercircuit 12, the equivalent circuit characteristic, such as thecapacitor, can be charged through the use of the rectified DC voltage 18for use in powering the visual indicator 20.

Example 11

Alternatives for the visual indicator 20 can include other suitableequivalent circuit characteristics. A possible constraint on the visualindicator 20 is that it needs relatively low power or ultralow power,since the ability for the electret 6 to provide substantial current maybe limited. However, many such visual indicators 20 are already designedto consume relatively low power or ultralow power.

FIG. 2 shows an indicator system 32 for an AC power bus 34 including anelectret 36 operatively associated with the AC power bus 34. Theelectret 36 includes an output 38 having an AC voltage 40 when the ACpower bus 34 is energized, and an indicator, such as an example visualindicator 50, comprising an input 52 electrically interconnected withthe output 38 of the electret 36 and an indication output 53 responsiveto the AC voltage 40 of the output 38 of the electret 36. The electret36 and the power bus 34 may be the same as or substantially similar tothe respective electret 6 and the power bus 4 of FIG. 1.

In FIG. 2, the visual indicator 50 needs to be powered by an AC voltagesimilar to what comes directly out of the electret 36 when it isactuated by the AC power bus electric field. In this case, no rectifiercircuit is employed.

Example 12

The indicator systems 2,32 of FIGS. 1 and 2 provide a safety functionfor, for example and without limitation, electrical control enclosures(e.g., without limitation, motor control centers (MCCs)) by indicating(e.g., without limitation, to a maintenance worker, electrician ortechnician) (e.g., without limitation, through a suitably high-contrastindicator) that a power bus 4,34 has been energized (e.g., by an appliedAC voltage, even though electrical current is not necessarily flowing orregardless whether a load is electrically connected). The disclosedconcept provides an indicator to alert people about an energized powerbus and therefore avoid accidental or unaware-based contact that couldotherwise cause severe injury or death.

Example 13

The indicator systems 2,32 of FIGS. 1 and 2 make use of the AC electricfield that is generated in the space around a power bus 4,34 that isenergized. These employ the generated electric field to “turn-on” anelectret 6,36 that is susceptible to the electric field. The electret6,36 is held in a structure that allows for the electric field of theenergized power bus 4,34 to interact with the self-charged, self-fieldof the electret in a manner that actuates the electret. For example andwithout limitation, in combination with a suitable visual indicator,this allows for a non-lighted, high-contrast visual indication of“turn-on” status.

Example 14

The indicator systems 2,32 of FIGS. 1 and 2 harvest energy from an ACpower bus electric field through use of an electret 6,36. The charge ofthe electret is acted on by the AC electric field to stress the electretmatrix, which in turn responds through its piezoelectric characteristicsto output a corresponding AC voltage 10,40, which actuates an indicatorto provide an indication of the energized AC power bus.

Example 15

The indicator systems 2,32 of FIGS. 1 and 2 generate useable energy froman energized power bus 4,34 (e.g., by an applied voltage even thoughelectrical current is not necessarily flowing or regardless whether aload is electrically connected) and employ the same to provide anindication of the energized AC power bus.

Example 16

The indicator systems 2,32 of FIGS. 1 and 2 interact with an energizedpower bus 4,34 through an electric field as opposed to a magnetic fieldthat is generated if current is flowing through the power bus. Hence,this solves the problem of monitoring an energized power bus even ifcurrent is not flowing (e.g., without limitation, a downstream circuitbreaker is open; the downstream load is disconnected). Thisadvantageously provides a very beneficial result since an energizedpower bus could have a voltage (and an associated electric field)present without having current flowing and still be a danger to a personwho accidentally touched or approached the power bus.

Example 17

For the indicator system 32 of FIG. 2, the input 52 of the visualindicator 50 is powered directly from the AC voltage 40 of the output 38of the electret 36. For the indicator system 2 of FIG. 1, the input 22of the visual indicator 20 is powered indirectly through the rectifiercircuit 12 from the AC current voltage 10 of the output 8 of theelectret 6.

Example 18

The electrets 6,36 can be stand-alone devices in electricalcommunication with the rectifier circuit 12 and/or the visual indicators20,50 (and any associated electronics (not shown)). Alternatively, theelectrets 6,36 can be part of a molded or a conventional housing (notshown) which contains some or all of the rectifier circuit 12 and/or thevisual indicators 20,50 (and any associated electronics (not shown)).The visual indicator 20 is actuated by the DC output voltage 18 of therectifier circuit 12. Alternatively, the rectifier circuit 12 is notrequired and a suitable indicator, such as the example visual indicator50, that is actuated by the AC output voltage 40 of the electret 36 canbe employed.

While specific embodiments of the disclosed concept have been describedin detail, it will be appreciated by those skilled in the art thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limiting as to the scope of the disclosedconcept which is to be given the full breadth of the claims appended andany and all equivalents thereof.

What is claimed is:
 1. An indicator system for an alternating currentpower bus, said indicator system comprising: an electret operativelyassociated with said alternating current power bus, said electretcomprising an output having an alternating current voltage when saidalternating current power bus is energized; a rectifier comprising aninput electrically interconnected with the output of said electret andan output having a direct current voltage responsive to the alternatingcurrent voltage of the output of said electret; and an indicatorcomprising an input electrically interconnected with the output of saidrectifier and an indication output responsive to the direct currentvoltage of the output of said rectifier.
 2. The indicator system ofclaim 1 wherein said electret is an electret device.
 3. The indicatorsystem of claim 1 wherein said electret is made of an electret materialsolution.
 4. The indicator system of claim 1 wherein said electret ismade from a material selected from the group consisting of an organicpolymer electret material, and an inorganic electret material.
 5. Theindicator system of claim 1 wherein said electret is coupled to saidalternating current power bus.
 6. The indicator system of claim 1wherein said rectifier is selected from the group consisting of a diode,a full wave bridge, and an integrated device.
 7. The indicator system ofclaim 1 wherein the indication output of said indicator is activeresponsive to the direct current voltage of the output of said rectifierwhen said alternating current power bus is energized.
 8. The indicatorsystem of claim 7 wherein said alternating current power bus has analternating current flowing therethrough.
 9. The indicator system ofclaim 7 wherein zero current flows through said alternating currentpower bus.
 10. An indicator system for an alternating current power bus,said indicator system comprising: an electret operatively associatedwith said alternating current power bus, said electret comprising anoutput having an alternating current voltage when said alternatingcurrent power bus is energized; a rectifier comprising an inputelectrically interconnected with the output of said electret and anoutput having a direct current voltage responsive to the alternatingcurrent voltage of the output of said electret; and an indicatorcomprising an input electrically interconnected with the output of saidrectifier and an indication output responsive to the direct currentvoltage of the output of said rectifier, wherein said indicator is anon-lighted, contrast visual indicator selected from the groupconsisting of printed electronics, electrochromatic inks, and electronicink.
 11. A power system comprising: an alternating current power bus; anelectret operatively associated with said alternating current power bus,said electret comprising an output having an alternating current voltagewhen said alternating current power bus is energized; and an indicatorcircuit comprising an input electrically interconnected with the outputof said electret and an indication output responsive to the alternatingcurrent voltage of the output of said electret, wherein said indicatorcircuit comprises a rectifier comprising an input electricallyinterconnected with the output of said electret and an output having adirect current voltage responsive to the alternating current voltage ofthe output of said electret, and an indicator comprising an inputelectrically interconnected with the output of said rectifier and anindication output responsive to the direct current voltage of the outputof said rectifier.